CHECK LIST OF FISHES d 



the deep sea, of most of the continents, and of fossil beds. The un- 

 exampled explorations of Eigenmann in South America belong to 

 this period, as also the records of Boidenger of the fishes of South 

 Africa and the varied researches of Regan in the rich material of the 

 British Museum. In this period the faunas of Australia, Japan, and 

 Siberia have been studied critically and successfully. Our knowledge 

 of fossil fishes is assuming definite form through the work of Wood- 

 ward, Zittel, Hay, Errol Ivor White, and othere who have given verte- 

 brate paleontology, as related to ichthyology, a constructive turn. 



We may again emphasize the distinction between the ancient and 

 modern periods in animal taxonomy. Beginning with 1758, the 

 date of Linnseus's Systema Nature, for 60 years a genus was usually 

 regarded merely as a convenient pigeonhole into which species w^ere 

 thrown. With Cuvier's Regne Animal (1817) came the conception 

 of arrangement "according to organization," or comparative anat- 

 omy. With Darwin's Origin of Species, 40 years later (1859), 

 zoologists began, though slowly at first, to realize that a classification 

 must be more than an inventory; that its basis must be genetic, and 

 that the problems involved in natural grouping are vastly more 

 complex than even great morphologists like Cuvier and Agassiz 

 had realized. To paraphrase a sentence of Elliott Coues, "genera 

 and species are but larger and smaller twigs of a tree, which we try 

 to arrange as nearly as possible in accordance with nature's rami- 

 fications." This view, applied to taxonomy, involves the extensive 

 subdivision of accepted genera, many of which wore in the highest 

 degree unnatural. Subdivision as practiced in the present paper 

 may go too far in some rases, but our material nuist be analyzed 

 first before we can group its parts in natural synthesis. No system 

 of naming can progress beyond the knowledge on which it rests. 

 We may emphasize here a statement attributed to Aristotle that 

 "one should never expect a degree of accuracy which the subject 

 matter does not permit." 



Each tendency in evolution, large or small, diverging from the 

 main current, should properly stand as a separate genus. 



The problem of subspecies among fishes is especially incomplete 

 and confused. Most of the marine species arc clearly definable and 

 not often subject to intergradations. Among the fresh-water forms, 

 all sorts of modifications occur. A species, in general, is a definable 

 group of related individuals that have run the gauntlet of life and 

 have endured. Among our river fishes we find species of dift'erent 

 types. There are numerous cases of species of compact though 

 often wide distribution, in which all individuals are, to all appear- 

 ances, similar. Plxamples of this type are the common perch {Ferca 

 fluviatilis), the common sucker {Catostomus commertionii), and the 

 minnows (Ericymba huccatn and Exoglosnum mnxillinqua) . Other 

 forms, which we have elsewhere called geminate or twin species, 

 may be distinct enough, having a few tangible characters of difference 

 in spite of general resemblance. These, for the most part, are set 

 apart from each other by barriers, their distinctness proportional to 

 the efiiciency of the barrier. Their origin may be due to the crossing 

 of these barriers by individuals from the mass of their kind, thus 

 acquiring a different environment with a different typo of selection. 

 Illustrations of geminate species set off by isolation may be found in 

 abundance, as among the trout of western America, and other species, 



